sea level change

• Isostatic changes:

  • Extra mass of ice and water on land during the glacial times is enough to cause subsidence of the lithosphere. 
  • 1000 m thickness of ice will change eventually causing 300 m of subsidence 
  • Sea level would appear to rise 
• Isostatic changes:

  • Peak glaciation  - eustatic sea level fall (rapid)
  • Isostatic sea level rise due to subsidence (slower)
  • But oceans have less water in them so ocean crust rises upwards giving further slow rise in sea level 
• Isostatic changes:

  • Deglaciation 
  • Eustatic - rise 
  • Isostatic - fall 
  • Ocean crust falls due to weight of oceans 
• Since end of last glacial:

  • Eustatic rise - using corals 
  • Isostatic change is still ongoing (NW Britain) under greater weight of glacier is rising 4 mm per year, tilting is causing southern England to sink
• Evidence of sea level rise:

  • Britain since Holocene has seen overall sea level rise - eustatic change greater than isostatic 
  • Sea level rise flooded glaciated valleys in north and river valleys in south - less land above sea level 
• Evidence of sea level rise:

  • Drowned glaciated valleys - fjord, lochs or sea lochs 
  • Steep sides and deep 
  • In Scotland rising sea levels have left islands 
  • Drowned river valley - rias - gentle with deepest channel in centre 
  • Submerged forests - remains of tree trunks, a result of flooding at end of glacial. 
  • Erosion of tidal zone - wave cut platform 
  • Old wave cut platforms form raised beaches 
  • Height above sea level today shows how much sea level has fallen 
  • Dating of fossilised shells found in raised beach deposits 
• River terraces and buried channels:

  • Sea level fall - river cuts further through flood plain alluvium deposits 
  • Leaves old flood plain behind - river terrace 
  • Can end up with multiple terraces with multiple phases of sea level fall 
  • River terraces are important - interglacial sites where humans and animals lived and were preserved 
  • Low energy on floodplains so fine grained 
• Sea level rise and river channels:

  • Sediment is deposited in river channels - buried channel